Each year, over 1 million abortions are performed in the US as a consequence of unintended pregnancy. Unintended pregnancies therefore have a significant negative impact on both the individual and society. Contraception is an effective method of reducing unintended pregnancies. One way to further reduce the rate of unintended pregnancies is to develop safe and effective methods for reversible male contraception. Hormone based approaches have been developed for use in men. However, these can have significant side effects including the length of time required for both contraception and its reversal. In theory, a specific inhibitor of spermiogenesis could be a powerful contraceptive method, as it should take effect, and be reversed, relatively quickly. Thus, a challenge for basic research is to improve our understanding of the gene products and pathways required for spermiogenesis so that some of these discoveries may be translated into novel approaches for male contraception. Towards this goal, we have used random insertional mutagenesis in mice to identify genes required specifically for mammalian spermatogenesis. Homozygous symplastic spermatids (sys) male mice are sterile due to a defect in spermatid-Sertoli cell adhesion just prior to spermatid elongation. The sys mutation involves a deletion of 1.2 Mb of mouse chromosome 14 that appears to contain only one, novel gene. This gene is predicted to encode a membrane-anchored structural protein with a proline rich N-terminus. We hypothesize that a defect in this novel gene is responsible for the sterility in sys homozygote males, that this gene functions in the Sertoli cell to mediate spermatid-Sertoli adhesion, and that inhibition of the genes function in fertile adult male mice could block spermatid development. Five specific aims are proposed to test this hypothesis. First, we shall generate male mice with a specific mutation of the novel gene and verify that they are sterile. Second, we shall use germ cell transplantation to investigate whether the function of the novel gene is required in germ cells or somatic cells within the testes. Third, we shall analyze the expression pattern and subcellular distribution of the gene product in testes using RNA in situ hybridization, immunohistochemistry and biochemical methods. Fourth, we shall investigate how the gene product functions by identifying proteins that interact with it in the testes. Finally, we shall investigate whether inactivation of this gene in adult fertile male mice can block spermiogenesis. The results of this basic research will provide information about a new gene product whose function is required for spermatid-Sertoli adhesion. They will also provide an assessment of the suitability of this novel gene product as a potential target for development of new methods of male contraception. [unreadable] [unreadable] [unreadable]